1. Field of the Invention
The present invention relates to a method and composition for coating metal workpieces with a corrosion-resistant coating. More particularly, the present invention relates to method and composition for rendering a vehicular brake rotor corrosion resistant. Even more particularly, the present invention concerns an alkali metal-silicate based coating composition and method of using same for rendering a vehicular brake rotor corrosion-resistant.
2. Prior Art
Metal parts are often used in industrial as well as automotive applications. Oftentimes, such metal parts encounter environments in which corrosion, due to salt spray or environmental exposure, may be a problem. Therefore, it is relatively common to coat such metal parts with a protective coating to inhibit corrosion from occurring.
Currently used methods of coating such metal parts ordinarily requires a cleaning step to clean oil, grease, etc. from the part, an intermediate pretreatment step, which normally involves pre-coating the metal part with zinc phosphate or similar treatment, and then a third step of applying the protective coating to the metal part.
This intermediate step of phosphating or otherwise treating (usually referred to as passivating is expensive and time consuming. Moreover, traditionally the subsequent coating composition must be compatible with the passivated surface.
Thus, even though numerous types of corrosion inhibiting coating compositions are known, a need still exists in the art for a method of coating metal parts in which the intermediate step of plating the metal workpiece with zinc phosphate or the like is eliminated in order to simplify the process and to cut down on the time required to coat metal workpieces.
Within the context of corrosion resistance one of the more difficult problems encountered is rust or corrosion of vehicular or automotive brake rotors on the braking surface, after the vehicle has been delivered the dealer and prior to customer purchase. Heretofore, it was believed that the coating of the braking surface of a brake rotor was to be avoided to preclude any deleterious or adverse effect on braking. Thus, previous brake rotor coatings were either removed at the factory prior to vehicle delivery or removed upon initial brake applications. Yet, the corrosion of the brake rotor surfaces and its accompanying "warranty" problems is expensive and time consuming. Thus, it is apparent that a major advance in the art would be achieved by a corrosion-inhibiting coating composition which could be effectively applied to the entire vehicular brake rotor while providing protection often from about fifty to about one hundred brake applications. It is to this to which the present invention is directed.